Positive impact of COVID-19 lockdown on heavy metals in groundwater and 1 possible health risks for human beings in an industrialized city of South India

31 In 32 concentration and biological parameters in the groundwater samples of Coimbatore city of South 33 India. The groundwater samples (n=15) were obtained from shallow-open wells before lockdown 34 (24-25 January 2020) and after lockdown (2-3 June 2020) periods. These samples were analysed 35 for heavy metals (Fe, Mn, Ni, Cr and Pb) and biological parameters ( E. coli, Fecal coliforms, Fecal 36 streptococci and Total coliforms ). Fe concentration was within the permissible limit but, the 37 concentrations of Mn, Ni, Cr and Pb were above the allowable limits for drinking uses as per the 38 WHO. However, after lockdown the number of samples crossing the cutoff limit had considerably 39 decreased (Mn: 2 to 0; Ni: 13 to 10; Cr: 7 to 5; Pb: 13 to 8). The spatial distribution of heavy metal 40 pollution index (HPI) revealed that 176.75 km 2 (67.4%) and 85.35 km 2 (32.6 %) areas fell under 41 unsuitable and very poor categories, respectively, during pre-lockdown period, whereas 138.23 42 km 2 (52.6 %), 118.98 km 2 (45.3%) and 4.89 km 2 (2.1%) areas fell under very poor, poor and good 43 categories, respectively, during post-lockdown period. Similarly, Total coliform, Fecal coliform 44 and E. coli had decreased distinctly due to the pandemic lockdown. Therefore, shutdown of small 45 and large-scale industries during the lockdown period had improved the groundwater quality. 46 Health risk assessment showed that 93%, 87% and 80% of pre-lockdown samples, and 87%, 80% 47 and 73% of post-lockdown samples possessed non-carcinogenic risks (HI > 1) for children, female 48 and male categories, respectively. writing-review and editing, and supervision. Aravinthasamy Palanisamy: data curation, 334 methodology, resources, writing-original draft and software. Shankar Karuppannan: formal 335 analysis and. Subramani Thirumalaisamy: writing-review and editing, methodology, and formal 336 analysis. Raj Setia: writing-review and editing.


INTRODUCTION
The precipitous growth of industrialization and urbanization in the last few decades has 55 severely contaminated the natural environmental components (soil, air, water, etc.) with various 56 pollutants throughout the globe (Rahman et al. 2020). Among different pollutants, heavy metals 57 are considered to be the most dangerous contaminants because of their toxic effects at higher 58 concentrations and persistence in natural components (Elumalai et al. 2017). The main origin of 59 the heavy metals in water is parent rock materials. The natural concentration of heavy metals in 60 water is usually low (Mukherjee et al. 2019), but their concentration increases many folds due to 61 anthropogenic activities (e.g. extensive agro-chemicals based agriculture, industrial and urban 62 wastewater discharges in water sources etc). Water contamination with heavy metals is a primary 63 environmental concern in both developed and developing countries (Khan et al. 2013). A infiltration of heavy metals to aquifers might lead to several health problems because of intake of 70 heavy metals via water used for drinking purposes (Balakrishnan and Ramu 2016). In addition to 71 health risks due to heavy metals, many bacterial diseases are transmitted through waste waters 72 discharged into groundwater system (Gao et al. 2020). Therefore, assessment of biological quality 73 of water is also important because several bacterial illnesses (like cholera, bacillary dysentery and 74 typhoid fever) are transmitted through contaminated water (Cabral 2010). Several studies 19 lockdown on heavy metals contamination and microbiological quality of water has not been 78 assessed.

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In India, industries were closed due to COVID-19 because the focus was on containing the 80 spread via quarantines and national lockdowns (Hamzelou 2020 contamination in groundwater will be reduced, but microbiological quality of groundwater will be 89 improved during and just after the COVID-19 lockdown period. Therefore, we studied the heavy 90 metal contamination and microbiological quality of groundwater before and after the COVID-19 91 lockdown period in Coimbatore (largest Industrialized city) region of southern India. In addition 92 to this, human health risks were also calculated and the multivariate statistics were used to identify 93 the probable source of metals in the groundwater of the city of Coimbatore before and after the 94 COVID-19 lockdown periods.

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Study area 97 Coimbatore is the largest industrial city in the state of Tamil Nadu and is also referred as 98 the state of Manchester. The study area is situated between the latitudes 10°52'30"N and 11° 99 4'30"N, and longitudes between 76° 51'0"N and 77° 3'0"N ( Figure 1). The total area is 262 km 2 . The average annual rainfall ranges from 550 to 900 mm, and temperature fluctuates from 19.8 to 101 35.9°C. The land use/land cover (Lu/Lc) of the area was classified using Landsat-8 satellite data 102 ( Figure 1). The major Lu/Lc cover is settlement (46.4%) followed by agriculture (23.7%), industry 103 (5.9%) and other classes like follow land (13.4%), water bodies (2.03%) and hills (8. 53%). The 104 major soil types in the region are red non-calcareous, red calcareous, black soil, and colluvial soil.

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The major industries are textile, dyeing, electroplating, petrochemicals, steel, building materials, 106 chemicals and fertilizers, plastic and sugar and metal casting. In the current situation, more than

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HPI was used to identify the impacts of distinct heavy metals on the quality of groundwater.

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The HPI was calculated using the equation 1 (Mohan et al. 1996).  The values of HItotal more than 1 indicates severe non-carcinogenic risk.

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Heavy metals in groundwater 180 Table 1 displays    76.2% of the total variances were extracted from three and four principal components, 308 respectively, in pre-and post-lockdown periods. The hazard index indicated that the number of 309 14 samples possessing non-carcinogenic risk (HI > 1) has reduced from 93% to 87%, from 87% to 310 80% and from 80% to 73%, respectively, for children, female and male categories due to the 311 lockdown effect. This shows children are more prone to non-carcinogenic risk than female and 312 male. The results suggest that heavy metal contamination in groundwater is mainly associated 313 with industrial effluents, sewage, sludge and dumping of municipal wastes. Though the 314 COVID-19 pandemic has improved the groundwater quality, this is not the solution to improve 315 the quality of groundwater as it has impacted millions across the world and has brought the 316 economy to a grinding halt. However, the results will be useful for devising the remediation 317 strategies to reduce the multi-metal contaminations in groundwater, and also the 318 epidemiological methods to prevent the human health risks. Further, the outcome of this study 319 insists the responsibilities of industrial, municipal and agricultural sectors to keep the 320 environment pollution free and to ensure the supply of potable water to the people of this city.

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Conflict of interest 322 The authors declare that they have no known competing financial interests or personal 323 relationships that could have appeared to influence the work reported in this paper.

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Funding: 325 The present work did not receive any financial assistance from any funding agency.

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Data Availability: Not applicable.